Photoelectric tube



1933- e. s. c. LUCAS PHOTO ELECTRI C TUBE Filed May 19, 1930 InventorGeorge S.C.-Lucas,

His Attorney Patented Nov. 7, 1933 PHOTOELECTRIO TUBE George S.C..Lucas, Rugby, England, assignor to General Electric Company, acorporation of New York Application May 19, 1930, Serial No. 453,651,and in Great Britain May 28, 1929 5 Claims. (01; 250-275) This inventionrelates to improvements in photo-electric tubes such as are used for thereproduction of sound from a sound record film. It is usual inreproducing sound from a film to cause the film to pass rapidly in frontof a narrow slit, a beam of light passing through the film and slit andfalling onto a photo-electric tube connected in a suitable amplifyingcircuit containing a sound reproducing device or loud speaker. In analternative method of reproduction the beam of light passing through thefilm is produced optically by means of a larger slit placed at somedistance from the film.

The essential feature of these methods of reproduction is that the widthof the pencil of light falling on the film shall not exceed onethousandth of an inch in order that a sound record containing notes of awave length of the order of .0035 of an inch will be faithfullyreproduced.

The object of the present invention is to provide an improved type ofphoto-electric tube and to that end it consists in constructing the tubewith a light-sensitive cathode of thin wire having a thickness at leastin one plane in the neighborhood of .001 of an inch in diameter. Animage of a portion of the film may thus be focussed onto the wire. Inthis way the only section of the film controlling the tube at anyinstant is the part, the image of which falls directly on the wire andsince the wire is only .001 of an inch wide, the result is equivalent tohaving a slit .001 of an inch wide in front of the film. The cathode ofthe tube may therefore consist of a fine wire of light-sensitivematerial, well known in the art, and the anode of a cylinder surroundingthe cathode having a longitudinal slit to allow the light to fall on thewire. As an alternative, the anode may be in the form of a half cylinderwith a portion at the back cut away to prevent light reflected from theanode from falling on the cathode or the inside may be blackened toprevent reflection.

Io enable the invention and the manner in which it is carried intoeffect to be readily understood, reference is directed to the followingdescription of the accompanying drawing, in which Figs. 1 to 4 showvarious constructions of a photo-electric tube in accordance with theinvention, and Fig. 5 illustrates the manner in which the tube may beused for reproducing sound from a photographic record thereof.

Referring to Fig. 1, I have shown the tube as consisting of an evacuatedtube 1 having the usual form of base 2, the electrodes being supportedfrom a pinch 3. In accordance with the invention, the cathode 4 consistsof a thin wire of lightsensitive material and having a diameter of theorder of .001" mounted concentrically within an anode 5,preferably ofcylindrical form having a longitudinal slit 6 through which light maypass to reach the cathode.

In place of the cylindrical form of anode shown in Fig. 1 I may use, ifdesired, an anode of semicylindrical formation, this construction beingequivalent to the use of a slit 6 of a width equal to the diameter ofthe anode.

In Fig. 2, the anode '7 is shown as consisting of two plates of curvedformation, having between them the slit 8 through which light may passto the cathode 4. These two plates may be so arranged as to constitute aportion of a cylindrical anode.

Fig. 3 represents an arrangement in which the two plates constitutingthe anode 9 are fiat instead of curved as in Fig. 2.

When the photo-electric tube is to'be used for reproduction from aphotographic record of sound waves by electrical means, it is desirableto have means for determining when the image of a portion of the soundrecord is accurately focussed 80. onto the cathode. In Fig. 4 this meansis shown as comprising plates 10 extending radially from the anode 11and located in the plane containing the cathode 4. An image of a portionof the record can thus first be formed on one of the plates before it iscaused to fall upon the cathode itself.

Instead of using a thin wire of the order of .001" in diameter as thecathode, I may use a light-sensitive ribbon having a thickness of theorder of .001. In this case the edge of the ribbon should be directedtowards the slit in the anode, that is to say, the plane containing thesmallest dimension of the cathode should be normal to the plane passingthrough the slit.

In Fig. 5 I have shown an arrangement in which the improvedphoto-electric tube may be used in reproducing sound from a photographicrecord thereof. This record is located on a film 12 and light from asource 13 is caused to pass through the film onto the cathode of thetube indicated at 14. A mask 15 restricts the light falling on the filmto a portion only thereof determined by the size of the opening 16 inthe mask. Suitable lenses shown at 17 and 18 may be used forconcentrating the light from the source onto the film and for forming animage of the illuminated portion of the film on the cathode of thephoto-electric tube 14. It is, of course, essential that the cathodeshould be arranged perpendicular to the direction of movement of therecord 12. 1,10

3. A photo-electric tube comprising a .linear light-sensitive cathodeand a cooperating. anode, said cathode having a thickness, at least inone plane, of the order of one thousandth of an inch.

4. A photo-electric tube comprising a linear light-sensitive cathodehaving a thickness, at least in one plane, of the order of onethousandth of an inch and a cooperating anode formed with a lon-.

gitudinal slit through which the light rays are adapted to pass in orderto reach the cathode, said slit being positioned to coincide with theplane perpendicular to the plane in which the thickness of the cathodeis measured.

5..A photo-electric tube comprising a linear light-sensitive cathodehavinga thickness, at least in one plane, of the order of one thousandthof an inch, and a cooperating anode formed with va-longitudinal slitthrough which the light rays are adapted to pass in order to reach thecathode,

, saidislitcbeing positioned to coincide with the plane perpendicular tothe plane in which the thicknessof'the cathode is measured, said anodebeing providedwith-a plate located in the same plane in which thethickness of the cathode is 1 measured.

GEORGE S. C. LUCAS.

